Quote Originally Posted by rspears View Post
As long as the furnace is not in your segregated paint area and you don't have a cold air return pulling from that area you would be fine to heat with the indirect propane furnace, blowing heated air into the paint area. The concentration of paint fumes has to get very high to be flammable, anyway, and you will be ventillating the area to clear fumes, right? Your concern about heat escaping through the non-insulated metal walls is the major issue - I have the same thing in my barn.
My shop is not divided at all and it is only 900sq feet. I suppose it would help to pull the air in from outside instead of the shop.